Electrode-supporting assembly for contact-start plasma arc torch

ABSTRACT

An electrode-supporting assembly for a contact-start plasma arc torch has an insulator that partially houses an electrode, and employs a spring-loaded plunger to bias the electrode to a forward position. The spring is engaged between the plunger and a contact element attached to the insulator, and may conduct electrical current to the electrode. The plunger, spring, and contact element are retained in the insulator when the torch is opened to replace the electrode, which is a consumable part. The electrode and the plunger have axially-engagable mating surfaces to assure good thermal and electrical conductivity therebetween. Conductivity can be further enhanced by forming the plunger of silver or a silver-bearing alloy. In some embodiments, a passage through the insulator is partitioned into forward and rear chambers, with the plunger, spring, and contact element trapped in the rear chamber.

FIELD OF THE INVENTION

The present invention relates to contact-start plasma torches, and moreparticularly to a novel structure for providing electrical connection ofa consumable electrode with a power supply.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,791,268 teaches a contact-start plasma arc torch wherethe electrode is biased forward by a plunger which resides in anenclosed structure; this structure is formed such that a significantportion of the electrode is not exposed to gas flow which would enhancecooling, and there appears to be little gas flow past the plunger.Additionally, the contact between the plunger and the electrode isprovided only across relatively small planar contact surfaces, which maybe susceptible to reduced contact due to any unwanted materialinterposed between these surfaces.

U.S. Pat. Nos. 8,035,055 and 8,115,136 teach a variety of electrodeconfigurations for contact-start plasma arc torches, as well as teachinga prior art electrode which employs a spring-loaded contact for thepower supply for biasing the electrode toward its forward position. Inthe prior art device cited in these patents, the electrode and contactremain engaged at all times. In basic embodiments of the inventiontaught in these patents, a spring is positioned between the electrodeand the contact to bias the electrode away from the contact. In theseembodiments, the electrode directly engages the contact only when in itsrear position, which is the position for sustaining the non-transferredpilot arc and the transferred cutting plasma arc. Unless the electrodeincludes the spring, the spring may be lost when the torch is opened tochange the electrode.

Perhaps to avoid the possibility of springs being lost when the torch isopened to change the electrode, these patents also teach severalembodiments that employ an electrode having a spring-loaded conductiveelement that is secured to the electrode, trapping the spring. Securingthe conductive element and spring to the electrode requires that thesecomponents be replaced with the electrode, increasing expense of theelectrode, which is a consumable part.

In still other embodiments, the electrode is installed via abayonet-style connection where the spring is positioned behind thefemale section of the bayonet element and thus trapped in the assembly.The electrode is provided with the male portion of the connection and,when inserted and locked in position, this portion contacts the spring.In another embodiment, the spring is retained by a fixed ring whichoverlaps part of the spring and a pair of prongs are positioned so as topass though the opening and engage the spring. Such a configurationprovides limited contact. While these latter solutions overcome theexpense of attaching the spring and a conductive element to theelectrode, it complicates the structure of the electrode, againincreasing expense of fabrication, and may limit air flow over thespring and the contacting portion of the electrode, thereby reducingcooling. These embodiments also appear to suffer from limited engagementbetween the spring and the electrode, thus limiting the effectiveness ofelectrical contact therebetween. These limitations may explain why theelectrode currently being commercially offered by the patentee is theembodiment shown in FIGS. 3A and 3B of the '155 and '136 patents, whichhas a spring and a conductive element secured to the electrode.

SUMMARY OF THE INVENTION

The present invention is for an electrode-supporting assembly for use incontact-start plasma torches to position and provide electrical contactfor an electrode while allowing it to be readily replaced. The assemblyincludes the structure for providing current to the electrode whileallowing it limited longitudinal motion, as discussed below.

The term “electrode” as used in the present application defines aconsumable element of the torch that can be readily be replaced when thenozzle of the torch is removed.

The plasma torch suitable for incorporating the present invention has acurrent-carrying cathode that connects to a power supply and terminatesin a power transfer surface. The torch has a torch recess for receivinga hollow insulator that slidably engages an electrode and introducespressurized gas into a chamber defined, in part, by a nozzle element. Aretaining element secures the nozzle with respect to the torch recess.The torch is designed to allow the electrode to move between a forwardposition where it contacts the nozzle element, at which time a currentis passed through the electrode to start the torch, and a rear positionspaced apart from the nozzle, to which the electrode is blown back bypressure of gas introduced through the insulator, creating the chamberfor developing and maintaining plasma. Initially, a pilot arc ismaintained from the electrode to the nozzle, developing a pilot plasmaarc. When the torch is brought in close proximity to a workpiece to becut, this non-transferred arc from the electrode to the nozzle elementtransfers so as to arc from the electrode to the workpiece, therebyestablishing a transferred plasma arc. The assembly of the presentinvention includes an insulator and electrode, as well as relatedelements to provide more positive electrical contact and improvedcooling of the electrode. The related elements allow for simplificationof the electrode, allowing it to be easily and inexpensively fabricated.

The insulator is formed of an electrically non-conductive material andis designed to be slidably inserted into the torch recess of the torchin place of the conventional swirl ring, and is retained therein in theconventional manner. Typically, the insulator is forcibly engaged by thenozzle element which, in turn, is secured by the retaining element. Theinsulator is provided with gas passages to introduce gas into a regionof the torch bounded, in part, by the nozzle element, in the same manneras a conventional swirl ring. This gas applies pressure to drive theelectrode to its rear position where it is spaced apart from the nozzle,as well as providing gas to sustain plasma, while the remainder of thegas flows backwards along the electrode, providing cooling.

The electrode of the assembly has a longitudinal axis, and a portion ofthe electrode resides within the insulator when in service. Theelectrode is movable from the forward position, where it is in contactwith the nozzle element of the torch, and the rear position, where theelectrode is displaced back from the nozzle element. The forwardposition serves as a starting position for the torch; when the electrodeis so positioned, a current can be passed through the electrode via aresilient element and, as the electrode is withdrawn away from contactwith the nozzle element, an arc is generated that initiates theformation of the pilot plasma arc. When the electrode is in this rearposition, the pilot arc is maintained between the electrode and thenozzle element with the principal current no longer being provided bythe resilient element. When the torch is subsequently brought into closeproximity to the workpiece, this non-transferred plasma arc istransferred from the nozzle element to the workpiece.

The electrode has a distal end, which includes an emissive element, anda proximal end. The proximal end of the electrode preferably terminatesin a non-planar electrode rear terminal surface. One such electrode rearterminal surface is a frustoconical protrusion or a frustoconical cup.

While the discussion below treats the terminal surface in terms ofcontinuous surfaces, it should be appreciated that the surface need notbe strictly continuous, and could be quasi-continuous. In either case, afrustoconical surface having an apex angle between 16° and 60° ispractical, and a more restricted range of angles from about 40° to 60°is felt to be particularly effective.

A plunger fabricated from an electrically conductive material alsoresides within the insulator when in service, positioned rearward of theelectrode. The plunger has a front contact surface that is configured soas to releasably mate with the electrode rear terminal surface; thesereleasable mating surfaces are configured such that they can be broughtinto mating engagement by translation along a longitudinal axis of theelectrode. Thus, when the electrode rear terminal surface is a concavesurface, the front contact surface of the plunger is a mating convexsurface. Having non-planar mating surfaces such as conical surfacesincreases the contact area between the electrode and the plunger toreduce the contact resistance and promote heat transfer, and conical orfrustoconical surfaces also provide centering to maintain the electrodeand the plunger aligned with each other. The plunger provides a heatsink for extracting heat from the electrode, in part since there isextensive contact between the plunger and the electrode, therebyproviding lower operation temperatures for the components during theoperation of the torch. The plunger terminates in a rear sectionterminating in a plunger rear surface.

Having a plunger that carries current to the electrode provides abenefit in that the electrode employed can have a very simple structureand can be readily replaced without requiring additional parts to bereplaced, as is required by several embodiments taught in U.S. Pat. Nos.8,035,055 and 8,115,136, where a resilient spring is employed to supplycurrent during start-up and this spring is trapped on the electrode by aconductive element. Securing the conductive element and spring to theelectrode requires these components to be replaced along with theelectrode, increasing expense of the electrode, which is a consumablepart. A basic embodiment of these patents lacks a spring-loadedconductive element, and thus does not require that the spring beattached to the electrode. However if not attached to the electrode, thespring is either attached to a cathode of the torch, making replacementof the spring difficult when necessary, or a loose element which may besubject to loss when the electrode is removed for replacement.

In other embodiments of the '055 and '136 patents where the conductiveelement is not incorporated into the electrode, such as those shown inFIGS. 12-15 of these patent in which the electrode is maintained inengagement with the spring by a bayonet coupling, special machining ofthe proximal end of the electrode is required; this limits the abilityto assure good electrical connection therebetween. The bayonetconnection may also reduce gas flow past the electrode and thus hampercooling.

In another embodiment of the above-referenced patents, shown in FIG. 16,posts protruding from the electrode pass through a restricted region ofthe passage in the insulator. This restriction serves to retain thespring in the insulator; however, it does so by complicating thefabrication of the electrode and reducing the contact area with thespring, which may limit the ability to assure an adequate arc to form apilot arc.

In some embodiments of the present invention, the plunger not onlyprovides a large surface for contacting the electrode but also isfabricated from silver or a silver alloy, which offers excellentelectrical and thermal conductivity and provides an interface betweenthe plunger and the electrode with low thermal and electricalresistance. The use of silver should also reduce the contact resistancebetween the spring and the plunger, thereby increasing the heatextraction from the spring in the case where the limiting temperature ofthe spring results from resistive (I²R) heating.

In some embodiments, the plunger is configured to extend beyond theouter diameter of the proximal end of the electrode so as to provide ageneral flow of cool gases thereacross. This extension further enhancesthe cooling of the electrode and thus should extend its useful life.Providing the plunger with enlarged surfaces that are configured todeflect the gas flowing backwards enhances the cooling action of theplunger by increasing flow across the surface of the plunger. Cooling ofthe plunger can be further enhanced when the plunger rear section has areduced cross section that results in a stepped profile; this stepincreases turbulence in the gas flow adjacent the plunger rear sectionand promotes mixing of the gas to increase cooling.

A contact element of an electrically conductive material is provided,which is attached to the insulator and configured to engage it in such amanner that the contact element is forcibly engaged against the powertransfer surface of the cathode of the torch when the insulator issecured in place by the retaining element. The contact element in theassembly of the present invention has an array of contact gas passagesthrough which gas flowing back along the electrode can pass, andterminates in a contact forward surface and a contact rear surface. Inmany embodiments, the contact forward surface is configured to mateagainst at least a portion of the plunger rear surface of the plungerwhen the electrode is in its rear position. The contact rear surface isengaged against the power transfer surface when the insulator isretained in position. The contact element can be readily secured inposition in the insulator by providing a press-fit.

The resilient element (spring) attaches to the contact element and tothe rear section of the plunger. Means for maintaining engagement of thecontact element, the plunger, and the spring are provided; this meansretains these elements within the insulator when the electrode isreplaced, preventing loss. In one embodiment, this means for maintainingcontact is provided by frictional engagement between the resilientelement, the plunger and the contact element.

In some embodiments, in addition to the frictional contact surfaces tobe engaged by the spring, the plunger and contact element can bethreaded together by mating the helix of the spring with mating helicalgrooves on the contact element and plunger.

Providing such positive engagement not only assures maintaining theseelements in contact during service so as to assure mechanicalconnection, but also assures good thermal contact between the spring andthe plunger. This thermal contact promotes heat transfer from the springto the elements to which it is connected to enhance dissipation of theheat resulting from resistive heating (I²R). In cases where the springis degraded by overheating due to resistive heating, which can result ineither corrosion or tempering of the spring, such frictional contact canresult in better heat dissipation and, in this way, reduce the potentialfor overheating of the spring, which might adversely affect itsresiliency.

In some embodiments the damage to the spring may result from temperingand/or corrosion of the spring caused by environmental heat to which thespring is exposed. The use of a silver plunger may also serve to reducethe temperature fluctuations of the spring.

In some embodiments, the means for maintaining engagement of the contactelement, the plunger, and the spring are provided, at least in part, bythe structure of the insulator. In such embodiments, the insulator has acentral band of reduced cross-section, providing a passage which isconstricted such that the plunger cannot pass therethrough. Thisconstriction provides a bifurcated passage having a passage forwardsection for receiving the electrode and a passage rear section forconstraining the plunger and the spring, although in many embodiments aportion of the plunger protrudes through the constricted band into thepassage forward section to engage the electrode. In some embodiments,the central band provides an opening having a cross section sufficientlylarge as to allow the proximal end of the electrode to enter. However,in all cases the opening must be sufficiently large as to provide aspaced-apart relationship between the electrode and the central band inorder to provide open space for air flow. The central band is positionedsuch that, when the contact element, spring, and plunger are installedin the insulator, the spring (resilient element) is maintained incompression and there is a gap between the plunger and the central bandto allow limited gas flow when the electrode is installed in the torchand is in its forward position and in contact with the nozzle of thetorch.

Means for maintaining a consistent rear position of the electrode areprovided. Consistent positioning of the electrode when the torch isoperating in the plasma generating mode helps to accurately position theelectrode with respect to the nozzle element to suit the desiredoperating conditions, as well as to avoid fluctuation in the volume ofthe plasma chamber. The details of these means for maintaining aconsistent rear position of the electrode are a function of the elementsthat are employed to provide the conductive path from the contactelement to the electrode, discussed below.

Means for providing a conductive path between the contact element andthe electrode when in the forward position and when in the rear position(these positions being discussed above) can be provided by variousstructures which will, in part, depend on the electrical connectionschemes. In all cases where the resilient element is electricallyconductive, at least part of the current passes through the resilientelement for both positions of the electrode.

In some embodiments, a conductive stranded element such as a twisted orbraided wire or cable (which is at least partially non-resilient) isconnected between the contact element and the plunger to pass at leastpart of the current. In such cases, proper sizing of the resilientelement and the conductive stranded element can assure sufficientcurrent to the electrode for operation in both its positions, whileallowing sufficient resiliency in the resilient element to assure thesmooth transfer between the two limit positions of the electrode whenoperating the torch. In these cases, the means to maintain a consistentrear position of the electrode can be provided in a variety of ways. Inone scheme, the means to maintain a consistent rear position of theelectrode is provided by having the resilient element be a compressionspring that is sized, relative to the other elements, such that movementof the electrode to its rear position causes the plunger to compress thecoils of the resilient element until the coils of the spring are inabutting contact. This stacked configuration of the spring serves as arigidly non-compressible cylinder for limiting the rearward motion ofthe electrode. In an alternative embodiment, where the conductivestranded element resides in an envelope defined by the resilient element(the coil), the conductive stranded element folds onto itself and resultin a conductive mass residing between the contact element and theplunger.

For many of the embodiments, current to the electrode when in its rearposition is provided, at least in part, through a direct path betweenthe contact element and the plunger. In such cases, abutting contactbetween the contact forward surface of the contact element and theplunger rear surface of the plunger can also provide the means formaintaining a consistent rear position of the electrode. In a similarscheme, the means for maintaining a consistent rear position for theelectrode can be provided by abutting contact between an insulatorinterposed between the plunger rear surface and the contact forwardsurface. However, in such cases an alternate conduction path such as astranded conductor as discussed above may be needed to assure sufficientcurrent flow. The use of an insulator may allow the plunger to besmaller in size, reducing the cost when it is fabricated from silver.The insulator is preferably attached to either the contact element orthe plunger, such as by a press-fit or a high-temperature adhesive.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1-3 are section views illustrating an electrode-supportingassembly for a contact-start plasma arc torch, the assembly forming oneembodiment of the present invention. FIG. 1 illustrates the assemblyinstalled into the torch with an insulator of the assembly secured intoa recess in the torch, and the remaining elements of the assemblyresiding at least partly in the insulator; securing the insulator inposition forces a contact element against a current-carrying cathode ofthe torch. FIG. 1 shows the assembly when an electrode is in a forwardposition where it contacts a nozzle element of the torch.

FIG. 2 is a partially exploded view of the assembly shown in FIG. 1,showing the individual components when removed from the torch. Theelectrode has a proximal end having a rear terminal surface formed as acavity which mates against a plunger having a matching front contactsurface, which in turn is engaged by a resilient element that biases theplunger and the electrode forward relative to the contact element thatis affixed to the insulator.

FIG. 3 shows the assembly shown in FIGS. 1 and 2 when in service, andwhen the electrode has been forced by gas pressure to a rear positionwhere it is spaced apart from the nozzle element to generate an arc; thedistance between these two positions of the electrode is exaggerated inthe figures for purposes of illustration. In this embodiment, current ispassed from the contact element to the electrode through the resilientelement and the plunger when the electrode is in the forward positionshown in FIG. 1, and also passes directly from the contact elementthrough the plunger when the electrode is in the rear position shown inFIG. 3, where surfaces on the contact element and the plunger are incontact. The contact of these surfaces also serves to provide aconsistent rear position of the electrode in this embodiment.

FIG. 4 is a section view of an embodiment that is similar to that shownin FIG. 1, with the exception that the assembly has a stranded conductorto carry electrical current between the contact element and the plungerto provide greater capacity to carry current to the electrode. In thisembodiment, the plunger and the contact element abut when the electrodeis in its rear position to assure a consistent rear position of theelectrode.

FIG. 5 is a section view of another embodiment that employs theconductor configuration shown in FIG. 4, but differs in that it employsan insulating element interposed between the plunger and the contactelement to define the rear position of the electrode and thus the lengthof the plasma chamber.

FIG. 6 is a section view of another embodiment similar to that of FIG.4; however, in this embodiment, the stranded conductor resides within anenvelope defined by the coils of the resilient element.

FIGS. 7-9 are section views illustrating another embodiment, which hasmany features in common with the embodiment shown in FIGS. 1-3, butwhich eliminates the need for a frictional fit to maintain the elementswithin the insulator when the electrode is removed. FIG. 7 illustratesthe embodiment before the electrode is brought into contact with theplunger, where the electrode has not been fully inserted into theinsulator. The insulator has a central band which partitions a passageinto a forward chamber, in which the electrode can be slidably engaged,and a rear chamber which constrains the resilient element and theplunger. The band has an opening of reduced cross section, which issized to prevent the plunger from passing therethrough, thereby assuringthat the resilient element and the plunger remain engaged at all times;the plunger of this embodiment has a protruding collar to assure that itis retained by the central band. This configuration of the insulator andthe plunger also enhances cooling by increasing the flow of coolinggases over the surface of the plunger.

FIG. 8 illustrates the same embodiment as shown in FIG. 7; however, atthis position the electrode and the plunger are fully engaged. Thereduced cross section of the insulator must be so configured that theplunger cannot pass through it. The size of the reduced cross sectionregion in this embodiment is shaped such the it can accommodate entry ofthe proximal end of the electrode therethrough as the electrode is blownback by gas pressure. The cross section must also be sufficiently largeas to provide a spaced-apart relationship between the electrode and theopening so that, in service, gas flows around the electrode when theelectrode is in its rear position. In this embodiment, a portion of theplunger can extend forward of the central band to aid in the alignmentof the electrode with the plunger when the electrode is replaced.

FIG. 9 illustrates the same embodiment as shown in FIGS. 7 and 8 whenthe electrode has, in part, passed through the reduced cross sectioncentral band of the insulator and the rear surface of the plunger hasengaged the contact element.

FIGS. 10 and 11 illustrate an embodiment similar to that of FIGS. 7-9,but where the forward surface of the plunger is extended so as to engagea reduced cross-section region of the insulator without requiring acollar, as employed in the earlier embodiment. This extended surface mayprovide less obstruction to gas flow through the reduced cross-sectionregion past the plunger.

FIG. 12 is a section view that illustrates an embodiment similar to thatshown in FIGS. 7-9, but where the electrode has a non-planar electroderear terminal surface that is a convex frustoconical surface, and theplunger has a non-planar front contact surface that is formed as amatching concave frustoconical cup.

FIGS. 13 through 15 illustrate an embodiment similar to that shown inFIGS. 7-9, but where the plunger is configured such that it engages thecontact element so as to limit rearward travel of the electrode beforethe proximal end of the electrode reaches the opening between thepassage forward section and the passage rear section. This embodimentalso illustrates a swirl ring that is formed as a separate piece, ratherthan as an integral part of the insulator.

FIGS. 16 and 17 illustrate an embodiment that is similar to that shownin FIGS. 13-15, but where the electrode geometry is such that theelectrode proximal end has a cross section greater than that of theopening and thus would prevent it from passing into the opening betweenthe passage forward section and the passage rear section independent ofits engagement with the plunger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 3 are section views illustrating an electrode-supportingassembly 100 for use in a contact start plasma arc torch 102 (onlypartially shown). The torch 102 can be similar to those torches taughtin U.S. Pat. Nos. 8,035,055 and 8,115,136 with the electrode-supportingassembly 100 replacing the conventional structure for supporting andproviding electrical current to an electrode. The torch 102 has acurrent-carrying cathode 104 (shown in FIG. 1) that connects to a powersupply (not shown) and has a power transfer surface 106 for contacting aconventional electrode. The cathode 104 is mounted in a torch bodyelement 108 that is configured with a torch recess 110 for receiving aconventional insulated swirl ring element. A nozzle element 112 can besecured onto the insulator and the torch body element 108 by a retainingelement 114 that threadably engages the torch body element 108.

The assembly 100 has an insulator 116 that is configured to be slidablyinstalled onto the cathode 104 so as to reside in the torch recess 110in place of the swirl ring/insulator that is conventionally employed.The insulator 116 is retained in place by engagement with the nozzleelement 112 when the retaining element 114 is tightened onto the torchbody element 108. The insulator 116 has an array of swirl gas passages117, configured as a conventional insulated swirl ring element, butdiffers from a conventional swirl ring element in having a contactelement recess 118 (best shown in FIG. 2), discussed below. Theinsulator 116 can be retained in the torch recess 110 by forcibleengagement of an O-ring 119, which is mounted in the insulator 116, withthe cathode 104.

The insulator 116 serves as part of the structure for positioning andsupplying electrical power to an electrode 120 having a longitudinalaxis 122, formed of a conductive material such as copper. The electrode120 is movable with respect to the insulator 116 between a forwardposition (shown in FIG. 1) and a rear position (shown in FIG. 3). Theelectrode 120 terminates at a distal end 124 (labeled in FIG. 2) havingan emissive element 126 embedded therein, and a proximal end 128 thatterminates at a non-planar electrode rear terminal surface 130. In thisembodiment, the electrode 120 has a spiral fin 132 that aids inextracting heat to cool the electrode 120. This electrode is a freestanding element and unencumbered by attachment to other elements, sothat it can be readily removed once the retaining element 114 and thenozzle element 112 are removed from the torch body element 108. Theremoval of the electrode 120 can be done while leaving the rest of thestructure of the assembly 100 intact.

The electrode rear terminal surface 130 of the electrode 120 is aconcave surface, forming a cavity. In this embodiment, the electroderear terminal surface 130 is symmetrically disposed about thelongitudinal axis 122 and terminates at the proximal end 128. Theelectrode rear terminal surface 130 increases in cross section as itapproaches the proximal end 128 of the electrode. In the assembly 100,the electrode rear terminal surface 130 is frustoconical, providing acontinuous surface. The cone section defining the electrode rearterminal surface 130 can be formed by rotation about the longitudinalaxis 122 of a line segment inclined with respect to the axis 122 so asto define a cone having an apex angle α measuring between about 16° and60°, and more preferably between about 40° and 60°. An apex angle ofabout 50° is felt to provide a desirable area of contact whilemaintaining the angle α sufficiently large as to reduce the tolerancesrequired to provide accurate longitudinal positioning of an elementmated against the electrode rear terminal surface 130, as discussedbelow.

The electrode-supporting assembly 100 also has a plunger 136, which isagain fabricated from a highly conductive material. The plunger 136 forthis embodiment can be fabricated from silver or silver-based alloy,resulting in high thermal and electrical conduction across theinterfaces between the plunger 136 and adjacent elements. The plunger136 has a plunger front section 138 (again, labeled in FIG. 2) having anon-planar plunger front contact surface 139, and a plunger rear section140 (best shown in FIG. 2) that terminates in a plunger rear surface142. The plunger front contact surface 139 is configured to mateablyengage the electrode rear terminal surface 130, and thus is convex andfrustoconical in this embodiment. While frustoconical surfaces (130,139) are shown, it should be appreciated that other surface shapes couldbe employed. These non-planar mating surfaces should enhance thermal andelectrical conduction compared to the use of planar surfaces due to theincreased contacting surface area. To allow the electrode 120 to bebrought into mated engagement with the plunger 136, the mating surfacesshould be configured so as to avoid any obstructions that would preventthem from being brought into engagement by translation along thelongitudinal axis 122. For frustoconical surfaces (130, 139), definingthe cone to have an apex angle α of at least about 16° will preventbinding, allowing the surfaces (130, 139) to provide non-planarreleasably mateable surfaces that can be readily released fromengagement when the electrode 120 is replaced.

In cases where trapped air is likely to be a concern, a plunger passage144 such as a drilled hole can be provided, which passes from theplunger front section 138 through the plunger rear surface 142, to allowescape of air trapped between the plunger front contact surface 139 andthe electrode rear terminal surface 130. Alternative structures toprovide a path for escape of trapped air, such as one or more grooves inone or both of the mating surfaces (130, 139) could be employed.

A contact element 146 formed of an electrically conductive materialattaches to the insulator 116 so as to reside in the contact elementrecess 118; preferably, the contact element 146 is press-fitted into theinsulator 116.

The contact element 146 has an array of gas passages 148 therethrough,and has a contact forward surface 150 and a contact rear surface 152.The contact element 146 is configured such that, when the insulator 116is secured in the torch recess 110 by the nozzle element 112 and theretaining element 114, the contact rear surface 152 is forcibly engagedagainst the power transfer surface 106 of the cathode 104. This forcibleengagement provides a more positive contact with the cathode 104 than inmany of the embodiments taught in the '055 and '136 patents, which relyon spring pressure to provide such contact. The contact forward surface150 is provided on a contact forward section 154 of the contact element146.

A resilient element 156 connects between the plunger 136 and the contactelement 146, and in this embodiment the resilient element 156 is acoiled compression spring. The resilient element 156 engages the plungerrear section 140 and the contact forward section 154, serving to biasthe plunger 136 into contact with the electrode rear terminal surface130 when the electrode 120 resides in the torch 102 and is constrainedtherein by the nozzle element 112, thereby biasing the electrode 120 toits forward position shown in FIG. 1. In this position, contact of theelectrode 120 with the nozzle element 112 allows current passed throughthe electrode 120 to the nozzle element 112 to complete a circuit. Gasis subsequently introduced through the insulator 116 and pressurizes theregion bounded by the nozzle element 112 and the distal end 124 of theelectrode 120; this pressure forces the electrode 120 back against thebias of the resilient element 156 to its rear position, shown in FIG. 3(the distance traversed by the electrode 120 is exaggerated in thefigures for purposes of illustration). As the electrode 120 is movedaway from the nozzle element 112, the current results in an arc formingtherebetween, this arc heating the gas in the bounded region to generatea plasma, the bounded region surrounding the distal end 124 serving as aplasma chamber 158. The rearward movement of the electrode 120 moves theplunger 136, which is engaged with the electrode 120, forcing theplunger 136 to move towards the contact element 146, compressing theresilient element 156. Means for maintaining engagement of the plunger136, the resilient element 156, and the contact element 146 with eachother are provided in this embodiment by configuring the plunger rearsection 140 and the contact forward section 154 such that they arefrictionally engaged by the resilient element 156. That is the resilientelement 156 is frictionally engaged with both the plunger 136 and thecontact element 146. The frictional force is sufficient that the plunger136 remains in place within the insulator 116 and thus within the torchrecess 110 when the torch 102 is opened and the electrode 120 isremoved.

In a similar embodiment to that shown in FIGS. 1-3, the plunger and thecontact elements have threads configured to threadably engage theresilient element with the plunger and the contact element.

To stabilize the volume of the plasma chamber 158 when the torch 102 isoperating in either a non-transferred arc or transferred arc mode, meansfor providing a consistent rear position of the electrode 120 areprovided. In this embodiment, the plunger 136 and the contact element146 are configured such that the plunger rear surface 142 of the plunger136 engages the contact forward surface 150 of the contact element 146when the electrode 120 is moved backwards to the rear position. Itshould be noted that this position is maintained not only during thetransferred arc mode of operation, but is needed to maintain a stablenon-transferred arc mode.

The contact element 146 is provided with a vent groove 160 across thecontact forward surface 150, positioned to communicate with the plungerpassage 144 to provide a path for escape of heated air when the plunger136 and the contact element 146 are in abutting contact. It should beappreciated that such a vent groove could alternatively be provided onthe plunger 136.

Means for providing a conductive path between the contact element 146and the electrode 120 when in the forward position and when in the rearposition are provided to carry electrical current from the power supplyof the torch 102 to the electrode 120. In the electrode-supportingassembly 100, the means for providing a conductive path include theresilient element 156, which conducts all the current to the electrode120 when the electrode 120 is in the forward position shown in FIG. 1(where there is contact between the electrode 120 and the nozzle element112), and includes the engagement of the plunger rear surface 142 andthe contact forward surface 150 when the electrode 120 is in its rearposition. It should be noted that this rear position is the dominantposition for the electrode, and is even the position for the stabilizedpilot arc mode. In both positions, the current is conducted from theplunger 136 to the electrode 120 via the contact between the plungerfront contact surface 139 of the plunger 136 and the electrode rearterminal surface 130 of the electrode 120. Thus, in the pilot ortransferred arc mode of operation where the electrode 120 is in its rearposition, the engagement of the plunger 136 and the contact element 146provides both stabilization of the rear position of the electrode 120and a conductive path from the contact element 146 to the plunger 136,which in turn conducts current to the electrode 120. Due to therelatively large contact surfaces (142, 150), the current passed to theelectrode 120 in the rear position through the latter path isconsiderably greater than the current supplied via the resilient element156, and the reduced current as well as heat transfer to the plunger 136and the contact element 146 protects the resilient element 156 fromoverheating that might otherwise damage its resilient character.

In addition to the tempering problems degrading the resiliency of thespring 156 by resistive heating of the spring, the spring 156 is subjectto heating through conduction of heat from the electrode 120 through theplunger 136 to the spring 156. Further heating may be caused by the gaspassing over the spring 156 may be sufficiently hot to result in similardeterioration of performance with use. Also, the gas passing over thespring 156 may degrade the spring 156 by corrosion if the gas issufficiently heated.

FIG. 4 is a section view of an electrode-supporting assembly 200 that issimilar to the electrode-supporting assembly 100 shown in FIG. 1, havinga insulator 202, an electrode 204, a plunger 206, a contact element 208,and a resilient element 210. In this embodiment, a supplementalconductor 212 is provided that connects directly between the contactelement 208 and the plunger 206. The supplemental conductor 212 ispreferably a stranded cable to provide a high degree of flexibility. Thesupplemental conductor 212 can provide the means for providing aconductive path between the contact element 208 and the electrode 204via the plunger 206 when the electrode 204 is in the forward positionand in the rear position, either alone or in combination with theresilient element 210.

Since the supplemental conductor 212, either alone or in combinationwith the resilient element 210, can carry all the current from thecontact element 208 to the plunger 206 when operating in either mode,the plunger 206 and the contact element 208 need not be configured toengage when the electrode 204 is in the rear position. However, thecontact scheme illustrated the embodiment shown in FIG. 4 does not inand of itself assure that the electrode 204 is stabilized when a torchin which the assembly 200 is employed is operating in plasma-generatingmode. Alternate structure for providing means for providing a consistentrear position of the electrode may be needed. One such means could beprovided by configuring the resilient element 210 such that its coilsare completely collapsed and contact each other when the resilientelement 210 is compressed as the electrode 204 moves to its rearposition. Such a scheme may be more practical when the resilient elementis formed by machining away a tubular element, in which case theresilient element may be formed integrally with the contact element.However, the requirement of the resilient element 210 may increase itscost of fabrication and may provide only limited stability.

FIG. 5 is a section view of another embodiment of the present invention,an electrode-supporting assembly 250, which again has a insulator 252,an electrode 254, a plunger 256, a contact element 258, a resilientelement 260, and a supplemental conductor 262. However, the assembly 250differs from the electrode-supporting assembly 200 in the structure thatis employed to provide means for providing a consistent rear position ofthe electrode 254. In the electrode-supporting assembly 250, aninsulator 264 is interposed between the plunger 256 and the contactelement 258. The insulator 264 is attached to either a rear section 266of the plunger 256, as shown in FIG. 5 and discussed below, or to acontact forward surface 268 of the contact element 258. The insulator264 can be formed of a suitably rigid, non-conductive material such asVespel® plastic, and can be attached to the plunger 256 by a frictionfit or a high-temperature adhesive such as Loctite® Super Glue ULTRA GelControl. Alternatively, a non-conductive material can be deposited ontoa rear surface of the rear section 266 of the plunger 256 to form theinsulator 264. Similar techniques can be employed when the insulator 264is to be attached to the contact element 258 rather than to the plunger256.

The insulator 264 has a rearward-facing insulator bearing surface 270.When the electrode 254 is moved from its forward position to its rearposition, the insulator bearing surface 270 is brought into engagementwith the contact forward surface 268, and the engagement of thesesurfaces (268, 270) provides stabilization of the plunger 256 and theelectrode 254 in a manner similar to that of the surfaces (142, 150) ofthe electrode-supporting assembly 100 discussed above.

The attachment of the insulator 264 to the plunger 256 may block aplunger passage 272 extending through the plunger 256. To extend theplunger passage 272, the insulator 264 is provided with an insulatorpassage 274.

While the embodiment shown in FIG. 5 employs an insulator interposedbetween the plunger and the contact element to limit rearward positionof the electrode, it should be appreciated that alternate structures forphysically limiting the rearward motion of the electrode withoutrequiring direct contact between the plunger and the contact elementcould be employed, particularly when a supplemental conductor isprovided. For example, the insulator could be provided with projectionsthat are configured to be engaged by the electrode and/or the plunger toblock further rearward motion once the electrode has reached itsspecified rear position.

FIG. 6 is a section view of an electrode-supporting assembly 300 whichis again similar to the electrode-supporting assembly 200 shown in FIG.4, but again differing in the means for providing a consistent rearposition of an electrode 302. Again, a plunger 304 and a contact element306 engage a resilient element 308 and are also connected together by asupplemental conductor 310, these elements all residing within ainsulator 312. In the electrode-supporting assembly 300, thesupplemental conductor 310 resides within a cylindrical envelope definedby the resilient element 308.

FIGS. 7-9 are section views illustrating an electrode-supportingassembly 350, which forms another embodiment of the present invention,having many features in common with the electrode-supporting assembly100 shown in FIGS. 1-3. The electrode-supporting assembly 350 again hasan electrode 352 engaged by a plunger 354 which in turn is engaged by aresilient element 356, which in the case is a conductive spring. Withthe assistance of the resilient element 356, the plunger serves to biasthe electrode 352 forward as well as provide an electrical current pathto the electrode 352. This embodiment eliminates the need for africtional fit of the plunger 354 with a resilient element 356, as wellas a frictional fit between the resilient element 356 and a contactelement 358 to maintain the plunger 354 and the resilient element 356 inplace in an insulator 360 when the electrode 352 is removed. While abinding fit is not required to retain the plunger 354, it may still bedesirable to assure electrical contact between these elements. In thisembodiment, the insulator 360 incorporates a swirl ring and has apassage 362 therethrough, which traverses the length of the insulator360.

FIG. 7 illustrates the electrode-supporting assembly 350 when theelectrode 352 is removed from contact with the plunger 354. The passage362 through the insulator 360 is provided with a band 364 having areduced cross section that forms a band opening 366, which partitionsthe passage 362 into a forward chamber 368 and a rear chamber 370. Theforward chamber 368 has a cross section such that the electrode 352 canbe slidably engaged therein. The plunger 354 in turn is provided with acollar 372 that is sized larger than the band opening 366; this sizingarrangement assures that the movement of the plunger 354 is restrainedsuch that the collar 372 and resilient element 356 are confined to therear chamber 370. Thus, the resilient element 356 biases the plunger 354so as to forcibly engage the collar 372 against the band 364, as shownin FIG. 7.

The collar 372 is positioned rearward of a front contact surface 374 ofthe plunger 354, which is configured to mateably engage an electroderear terminal surface 376 in a proximal end 378 of the electrode 352when the electrode 352 is installed so as to reside partially within theinsulator 360, as shown in FIGS. 8 and 9. While the collar 372 isprevented from passing through the opening 366 of the band 364, thefront contact surface 374 must extend forward sufficiently to allow theplunger 354 to bias the electrode 352 against a nozzle (not shown) ofthe torch into which the assembly 350 is installed. The insulator 360and the plunger 354 should be configured such that, when the electrodeis installed in a torch and a nozzle is in place, a gap (a) is providedbetween the band 364 and the plunger 354, as illustrated in FIG. 8. Thisgap (a) should be made sufficient in size to avoid restricting thebackward flow of cooling gas that passes a spiral fin 380 of theelectrode 352.

The proximal end 378 of the electrode 352 in this embodiment is sizedsuch that, when the electrode 352 is blown back to its rear positionwhere the proximal end 378 passes into or at least partly through theband opening 366, the electrode 352 and the band 364 remain in a spacedapart relationship to leave a gap (b) therebetween as shown in FIG. 9.This gap (b) is made sufficient to maintain free flow of gas between theband 364 and the electrode 352 when the electrode 352 has moved to itsrear position. In this embodiment, a portion of the front contactsurface 374 of the plunger 354 extends through the band 364 when thecollar 372 engages the reduced cross section band 364, thisforward-extending portion of the front contact surface 374 serving toaid in bringing the plunger 354 into axial alignment with the electrode352 so that the front contact surface 374 of the plunger 354 becomesproperly engaged with the electrode rear terminal surface 376 when theelectrode 352 is installed.

As with the assembly 100 shown in FIGS. 1-3, the plunger 354, theresilient element 356, and the contact element 358 are designed to allowthe plunger 354 to be forced by the electrode 352 (which is being drivenrearward by the gas pressure being introduced through the swirl ring)against the bias of the resilient element 356 until the plunger 354engages the contact element 358, as shown in FIG. 9. The engagement ofthe plunger 354 and the contact element 358 defines the rear position ofthe electrode 352, and this engagement again provides both means forproviding a consistent rear position of the electrode 352 and means forproviding a conductive path between the contact element 358 and theelectrode 352 when in the rear position. Means for providing aconductive path when the electrode 352 is in the forward position areprovided by the resilient element 356, but could include a supplementalconductor such as those discussed above.

An additional benefit of the collar 372 of the plunger 354 is that itshould act to deflect the rearward flow of cooling gas that has passedthrough the gap (b) between the electrode 352 and the band 364. Thisdeflection should increase the flow of cool gas across the surfaces ofthe plunger 354, thereby enhancing its ability to act as a heat sink toaid in cooling the electrode 352, with which the plunger 354 is inthermal contact. The collar 372 may further enhance cooling by providinga shoulder over which the gas flows, thereby increasing the turbulenceof the flow over the rear portion of the plunger 354 to promote mixingof the gas as it flows past the plunger 354.

FIGS. 10 and 11 illustrate an electrode-supporting assembly 350′ that issimilar to the electrode-supporting assembly 350 shown in FIGS. 7-9, butwhere the plunger 354′ lacks a collar 372. In this embodiment, the frontcontact surface 374′ of the plunger 354′ is extended, and the opening366′ of the reduced cross-section band 364′ of the insulator 360′ isconfigured to be engaged by the front contact surface 374′ to limitforward motion of the plunger 354′, while allowing a portion of thefront contact surface 374′ to pass through the opening 366′ of thereduced-cross section band 364′ for engagement by the electrode 352′.When the electrode 352′ is engaged with the plunger 354′ and the nozzleof the torch (not illustrated) is in place such that the nozzle engagesthe electrode 352′, the gap (a′) exists between the plunger 354′ and theband 364′ so as to allow gas to flow therethrough. The electrode 352′has also been sized such that, when it is blown back to its rearposition where it passes into the opening 366′, the resulting gap (b′)is sufficient for gas to flow therethrough.

FIG. 12 illustrates an electrode-supporting assembly 400 that sharesmany features in common with the electrode-supporting assembly 350discussed above. Again, the assembly has a insulator 402, an electrode404, a plunger 406, a resilient element 408, and a contact element 410,and the insulator 402 is formed with a band 412 to provide an opening414 having a reduced cross section.

In the assembly 400, the electrode 404 has a proximal end 416 that istapered to form a convex frusto-conical electrode rear terminal surface418. The plunger 406 has a plunger front contact surface 420 that isformed as a frustoconical cavity, shaped to mateably receive theelectrode rear terminal surface 418. The electrode 404 is configuredrelative to the band 412 so as to be insertable into engagement with theplunger front contact surface 420.

FIGS. 13-15 illustrate an electrode-supporting assembly 450 that formsanother embodiment of the present invention, and which has many featuresin common with the electrode-supporting assembly 350 shown in FIGS. 7-9.The assembly 450 again has an electrode 452 that engages a plunger 454which in turn engages a resilient element 456 that connects to a powercontact element 458, these elements (454, 456, 458) serving to provideelectrical power to the electrode 452 when biased to the electrode'sforward position by the resilient element 456. The electrode 452 mateswith the plunger 454 as is the situation with the earlier embodiments.An insulator 460 is provided, having a passage 462 therethrough. Thepassage 462 has a band 464 which partitions the passage 462 into aforward chamber 466 and a rear chamber 468. Again, the plunger 454 andthe resilient element 456 are trapped in the rear chamber 468.

This embodiment differs from the earlier electrode-supporting assembly350 in that the plunger 454 has a cylindrical extension 470 positionedbetween a frustoconical plunger front contact surface 472 and a collar474. This cylindrical extension 470 has a length L (labeled in FIGS. 14and 15) that is chosen to be sufficiently long as to prevent theelectrode 452 from entering an opening 476 (labeled in FIG. 13) definedby the band 464. This length L assures that a gap (a) remains free whenthe torch is operating, as illustrated in FIG. 14. The extension 470must also have the length L sufficient that a gap (b) is present whenthe electrode 452 is in its rear position, as shown in FIG. 15. Theseconditions assure flow of gas past the plunger 454 when gas isintroduced into the passage 462.

The insulator 460 of this embodiment does not include an integral swirlring, but rather has an insulator stepped forward edge 478 thatstabilizes a separate swirl ring 480, as best shown in FIG. 13.

FIGS. 16 and 17 illustrate an electrode-supporting assembly 450′ whichhas all the limitations of the electrode-supporting assembly 450illustrated in FIG. 13-15, but differs from the earlier embodiment inthat the electrode 452′ has a proximal end region 482 having anelectrode diameter D_(E) which is greater than an opening diameter D_(O)of the opening 476′; this geometry should increase the turbulence of theflow of the air over the plunger 454′ and thus should enhance the heattransfer between the air flow and the plunger 454′.

While the novel features of the present invention have been described interms of particular embodiments and preferred applications, it should beappreciated by one skilled in the art that substitution of materials andmodification of details can be made without departing from the spirit ofthe invention.

What I claim is:
 1. An electrode and electrode-supporting assembly foruse in a contact start plasma arc torch having, a current-carryingcathode communicating with a power supply and terminating in a powertransfer surface, a torch recess, a nozzle element, and a retainingelement for securing the nozzle element with respect to the torchrecess, the electrode and electrode-supporting assembly comprising: aninsulator slidably engagable into the torch recess and configured to beretained therein by the retaining element when securing the nozzleelement; an electrode having a longitudinal axis and residing at leastpartially in said insulator, said electrode being axially movablebetween a forward position for contacting the nozzle element to startthe torch and a rear position spaced apart from the nozzle element so asto maintain a plasma arc, said electrode terminating in, a distal endincluding an emissive element, a proximal end terminating at anelectrode rear terminal surface; a plunger fabricated from a conductivematerial and residing in said insulator, said plunger having, a plungerfront contact surface configured so as to be releasably mateable withsaid electrode rear terminal surface of said electrode, and a plungerrear section terminating in a plunger rear surface; a contact elementconfigured to engage said insulator and having, an array of gas passagestherethrough to allow gas flow through said contact element, a contactforward surface, and a contact rear surface, said contact elementengaging said insulator such that said contact rear surface is forciblyengaged against the power transfer surface of the cathode when saidinsulator is retained in the torch recess; a resilient element engagingsaid contact element and said plunger rear section; means formaintaining engagement of said plunger, said resilient element, and saidcontact element with each other, thereby assuring said plunger and saidresilient element are retained in said insulator; means for providing aconsistent rear position of said electrode; and means for providing aconductive path between said contact element and said electrode whensaid electrode is in the forward position; and means for providing aconductive path between said contact element and said electrode whensaid electrode is in the rear position.
 2. The assembly of claim 1wherein said electrode rear terminal surface and said plunger frontcontact surface are mateable non-planar surfaces.
 3. The assembly ofclaim 2 wherein said electrode rear terminal surface and said plungerfront contact surface are substantially frustoconical surfaces.
 4. Theassembly of claim 3 wherein said means for maintaining engagement ofsaid plunger, said resilient element, and said contact element isprovided by a frictional engagement of said resilient element with saidcontact element and with said rear section of said plunger.
 5. Theassembly of claim 2 wherein said means for maintaining engagement ofsaid plunger, said resilient element, and said contact element furthercomprises: a central band of said insulator having a cross section sizedto form an opening sized such that said plunger cannot passtherethrough, said central band defining a forward chamber, in which atleast a portion of said electrode resides, and a rear chamber, in whichsaid contact element, said resilient element, and at least a portion ofsaid plunger reside, said central band being positioned such that saidresilient element is maintained in compression.
 6. The assembly of claim5 wherein said opening in said band is sized so as to allow passage of aportion of said proximal end of said electrode therethrough whileleaving a gap for flow of gas thereabout.
 7. The assembly of claim 1wherein said resilient element is a conductive spring, and furtherwherein said means for providing a conductive path between said contactelement and said electrode when said electrode is in the forwardposition includes said conductive spring and said plunger.
 8. Theassembly of claim 7 wherein said means for providing a conductive pathbetween said contact element and said electrode when said electrode isin the forward position further comprises: a stranded conductorconnected between said contact element and said plunger.
 9. The assemblyof claim 7 further wherein said electrode, when in the rear position,forces said plunger to a position where there is physical contactbetween said contact forward surface of said contact element and saidplunger rear surface of said plunger, this contact providing said meansfor providing a consistent rear position of said electrode.
 10. Theassembly of claim 8 wherein said means for providing a consistent rearposition of said electrode is provided by a stacked condition of saidspring.
 11. The assembly of claim 8 wherein said means for providing aconsistent rear position of said electrode is provided by an insulatingmember provided on at least one of said plunger and said contact elementand positioned so as to reside therebetween.
 12. The assembly of claim 1wherein said insulator is a tubular element having a passagetherethrough, said passage having a central band which partitions saidpassage into a forward chamber configured such that said electrode canbe slidably engaged therein, and a rear chamber which restrains themovement of said resilient element and said plunger, said passage havingan opening defined by said central band that provides communicationbetween said forward chamber and said rear chamber, and further whereinsaid central band and said opening are configured so as to allow saidelectrode to engage said plunger when the torch is assembled, whileproviding a spaced apart relationship between said plunger and saidcentral band, and between said electrode and said central band.
 13. Theassembly of claim 12 further comprising: means for preventing saidelectrode from entering said opening.
 14. The assembly of claim 13wherein means for providing a consistent rear position of said electrodeis provided by contact between said plunger and said contact elementthat limits rearward travel of said plunger and said electrode whenengaged therewith, and further wherein said plunger has an extensionhaving a length L selected to block movement of said electrode into saidopening when said plunger contacts said contact element.
 15. Theassembly of claim 14 wherein said proximal end of said electrode has adiameter D_(E) that is larger than a diameter D_(O) of said opening. 16.The assembly of claim 15 wherein said plunger is fabricated from a metalselected from the group of: silver; and silver-based alloys.
 17. Theassembly of claim 1 wherein said plunger is fabricated from a metalselected from the group of: silver; and silver-based alloys.
 18. Anelectrode and electrode-supporting assembly for use in a contact startplasma arc torch having, a generally cylindrical torch recess having arecess proximal end and a recess distal end; a current-carrying cathodecommunicating with a power supply and terminating in a contact surfacelocated at the recess proximal end, and a nozzle element that can besecured relative to the torch recess so as to substantially close therecess distal end, the electrode and electrode supportelectrode-supporting assembly comprising: an electrode terminating in anelectrode distal end that includes an emissive element and an electrodeproximal end terminating at an electrode terminal surface, saidelectrode moving relative to the nozzle element between a forwardposition, where said electrode distal end contacts the nozzle element,and a rear position, where said electrode is spaced apart from thenozzle element; and an electrode-supporting assembly having, a hollowinsulator having a central axis, said insulator engaging the torchrecess so as to be retained therein, said insulator being configured topartially enclose said electrode while allowing said electrode to movetherein between the forward position and the rear position, saidinsulator being further configured to allow said electrode to be freelyremoved therefrom when the nozzle element is removed from being securedwith respect to the recess, a contact element fabricated from aconductive material and attaching to said insulator so as to reside atthe recess proximal end of the torch, said contact element furtherhaving, a contact element proximal surface that is positioned toforcibly engage the contact surface of the cathode when said insulatoris retained in the torch recess, and a contact element distal surface, aresilient element forcibly engaging said contact element distal surface,a plunger fabricated from a conductive material and having, a plungerproximal surface that forcibly engages said resilient element such thatsaid resilient element biases said plunger away from said contactelement, and a plunger distal surface that is configured to be axiallyengageable with at least a portion of said electrode terminal surface ofsaid electrode, this engagement causing said plunger to compress saidresilient element when said electrode is in the electrode distalposition, means for limiting movement of said electrode towards saidcontact element so as to define the rear position of said electrode,means for providing a conductive path between said contact element andsaid electrode when said electrode is displaced away from its rearposition, means for providing a conductive path between said contactelement and said electrode when said electrode is in the rear position,and means for maintaining said plunger and said resilient elementconnected to said contact element when said electrode is removed fromsaid hollow insulator.
 19. The assembly of claim 18 wherein saidelectrode terminal surface and said plunger distal surface arenon-planar surfaces.
 20. The assembly of claim 19 wherein said insulatorhas a passage therethrough, said passage having a central band whichpartitions said passage into a forward chamber configured such that saidelectrode can be slidably engaged therein, and a rear chamber whichrestrains the movement of said resilient element and said plunger, saidpassage having an opening defined by said central band that providescommunication between said forward chamber and said rear chamber, andfurther wherein said band and said opening are configured so as to allowsaid electrode to engage said plunger when the torch is assembled, whileproviding a spaced apart relationship between said plunger and saidband, and between said electrode and said band.